pH/Temperature-responsive behavior of amphiphilic block copolymer micelles prepared using two different methods.

The pH- and temperature-responsive behavior of amphiphilic block copolymer poly(L-lactide)-b-poly(2-(dimethylamino)ethyl methacrylate) (PLLA-b-PDMAEMA) in aqueous solutions is investigated using static and dynamic light scattering. Electrostatic force, hydrophobic interaction, and hydrogen bonding coexist in the system. Micelles with different structures are prepared using water addition (WA) and direct dissolution (DD) methods. The aggregation from loose micelles into large micellar clusters is observed above the transition temperature under basic conditions. Only micellar clusters from the DD method could disaggregate when temperature was decreased to 24.3 °C after heating. The behavior of the micelles prepared with the DD method indicates that only the outer parts of the PLLA-b-PDMAEMA chains in the corona are solvated.

Phase behavior of poly(sulfobetaine methacrylate)-grafted silica nanoparticles and their stability in protein solutions.

Biocompatible and zwitterionic poly(sulfobetaine methacrylate) (PSBMA) was grafted onto the surface of initiator-modified silica nanoparticles via surface-initiated atom transfer radical polymerization. The resultant samples were characterized via nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Their molecular weights and molecular weight distributions were determined via gel permeation chromatography after the removal of silica by etching. Moreover, the phase behavior of these polyzwitterionic-grafted silica nanoparticles in aqueous solutions and stability in protein/PBS solutions were systematically investigated. Dynamic light scattering and UV-visible spectroscopy results indicate that the silica-g-PSBMA nanoparticles exhibit an upper critical solution temperature (UCST) in aqueous solutions, which can be controlled by varying the PSBMA molecular weight, ionic strength, silica-g-PSBMA nanoparticle concentration, and solvent polarity. The UCSTs shift toward high temperatures with increasing PSBMA molecular weight and silica-g-PSBMA nanoparticle concentration. However, increasing the ionic strength and solvent polarity leads to a lowering of the UCSTs. The silica-g-PSBMA nanoparticles are stable for at least 72 h in both negative and positive protein/PBS solutions at 37 °C. The current study is crucial for the translation of polyzwitterionic solution behavior to surfaces to exploit their diverse properties in the development of new, smart, and responsive coatings.

Chromatographic mode transition from size exclusion to slalom chromatography as observed for chitosan.

Elution behavior of chitosan was studied using narrow-bore size exclusion chromatography (SEC) columns packed with 8 µm porous particles at different eluent flow rates. Delayed elution of the largest chitosan species from the columns was observed at high flow rates, which was attributable to strong chain deformation rather than chain degradation. In particular, a chromatographic mode transition from SEC to slalom chromatography (SC) was observed for high molar mass chitosan samples with abnormal elution behaviors, which originates from the coil-stretch transition of chitosan chains in elongational flow through the columns. By properly reducing the elongational rate in the columns via tuning the flow rate, particle size and column dimension, the chromatographic mode transition from SEC to SC for chitosan can be effectively suppressed.

Adsorption of poly(vinyl alcohol) on gel permeation chromatography columns depends on the degree of hydrolysis.

Both fully (98%) and partially (88%) hydrolyzed poly(vinyl alcohol) (PVA) are characterized by aqueous gel permeation chromatography (GPC) coupled with multi-angle laser light scattering. Polymer adsorption on hydrophilic GPC columns is observed for partially hydrolyzed PVA but not for fully hydrolyzed PVA, which is driven by the hydrophobic interactions between the residual acetate groups on PVA and the stationary phase. Desorption of these partially hydrolyzed PVA chains from the packing materials is monitored by decay of the light scattering signal. It is found that the desorption of these polymer chains from porous particles is non-exponential and follows stretched exponential kinetics with index 0.36. It is also shown that asymmetric flow field flow fractionation can be successfully used for the molar mass characterization of PVA, irrespective of the degree of hydrolysis.

Strategy to improve the characterization of chitosan by size exclusion chromatography coupled with multi angle laser light scattering.

Here we present SEC-MALLS study for chitosan samples with weight average molar mass Mw between 33 and 427 kg/mol on columns packed with 8 µm porous particles. A low injection concentration on the order of 0.1-0.2 mg/mL must be used to avoid overloading of the SEC columns, due to the extended coil conformation of cationic chitosan in the dilute acid buffer as compared to neutral polymers. Additionally, SEC must be performed at an eluent flow rate no more than 0.5 mL/min for high molar mass chitosan samples. At flow rates of 1.0 and 1.5 mL/min, the elution of the largest chitosan species is delayed, which leads to a distortion of the molar mass distribution towards lower molar mass region. Such an abnormal behavior is due to a chromatographic mode transition from SEC to slalom chromatography, originated from the coil-stretch transition of chitosan chains in elongational flow through the packed columns.

Analysis of interfacial phenomena of aqueous solutions of polyethylene oxide and polyethylene glycol flowing in hydrophilic and hydrophobic capillary viscometers.

Viscosities of aqueous solutions of five polyethylene oxide (PEO) samples with molar masses from 1.5 x 10(5) to 1.0 x 10(6) were carefully measured in a polytetrafluoroethylene (PTFE) capillary Ubbelohde viscometer in the concentration range from dilute down to extremely dilute concentration regions and compared with those of the same sample obtained from a glass capillary viscometer. At the same time, viscosities of aqueous solutions of three PEG samples in glass and paraffin-coated capillary viscosity were measured. The wall effects occurred in viscosity measurements for PEO and PEG aqueous solutions in different capillary viscometers were theoretically analyzed and discussed. It was found that different interfacial behaviors occurred in both hydrophobic and hydrophilic capillary viscometers respectively and the interfacial behaviors also exhibit molar mass dependence.